*6.2. Sputtering: Oxynitride and Oxide Coatings*

The deposition of AlCr-based oxynitride and oxide coatings through sputtering has been approached using both RF-sputtering [173,179,182,183] as well as HiPIMS techniques [170,175]. Systematic investigations of RF-sputtered Al-Cr-O-N coatings have shown that, depending on the gas composition (Ar, O2, N2), the total gas pressure and the Al/Cr ratio, coatings with a single phase or mixed phase are grown. These are a corundum-type α-(Al1−*x*,Cr*x*)2(O1−*y*,N*y*)3 structure and a CrN-type fcc-(Al1−*x*,Cr*x*)(O1−*y*,N*y*) structure, as well as a mixed-phase composition of both single phases [173,183]. The corundum phase can contain up to 3 at.% nitrogen [138,183].

The coating composition and structure with a given sputtering target composition are strongly dependent on the sputtering mode. Different Al/Cr ratios, deposition rates, and oxygen contents were reported for the comparison of DC magnetron, HiPIMS and a hybrid mode employing both [175]. Thick oxynitride coatings, thicker than 35 μm, were deposited by gas-flow sputtering [170].
